Overhead roll-up doors provide resistance to high winds or wind loads and/or air pressure applied to a door panel when in a partially or fully closed position. These doors are typically guided up and down in side columns or vertical guide assemblies which include a vertical path of travel for the door panel which selectively permits and prohibits access to an opening or passageway. Wind load when the door is in a substantially closed or fully closed position is particularly problematic, because as is known in the art, the wind load increases as the door panel approaches a fully closed position. As more of the door panel is exposed, a greater surface area of the door panel may become “impacted” by the wind creating the load, thereby dramatically increasing the total load on the door.
In addition to having to account for wind load resistance, these doors may also be installed in high-traffic areas with the potential to be impacted by objects when the door is opening or closing—a necessitating that the door panel maintain a particular level of breakaway-ability in response to such an impact. In order to avoid damage to the door (from, for example, the surrounding structure, individuals near the door, and any objects striking the door), overhead roll-up door panels are typically designed to disengage from the side columns and deviate from the path of travel when impacted by an external force to either a front or back face of the door panel. While impacts may occur at any point while the door is opening or closing, typically these impacts occur at heights greater than two to four feet as the door is opening or closing as individuals or objects attempt to sneak under a closing door or approach an opening door too quickly before it is out of the passageway.
In order to provide rigidity to the door panel, facilitate the proper travel of the door panel in the vertical path, and provide additional resistance to wind load (or air pressure) and other external impacts, overhead roll-up doors may include a weighted “bottom bar” attached proximate a lower or leading edge of the door panel. Such bottom bars typically extend horizontally across the bottom of the door panel a distance approximately 1″-2″ less than the distance between the side columns and a distance approximately 2″-6″ less than the width of the door panel. In an attempt to further enhance wind load resistance and guidance and engagement with the side columns, bottom bars may include an extension, like for example flexible ultra-high molecular weight (“UHMW”) plastic tabs, that extend into the vertical path of travel, engaging the side columns. These tabs are typically designed to be rigid enough to provide some resistance to air pressure, however, they must be flexible enough to allow the bottom bar to disengage from the side columns should an object impact the bottom bar or door panel. If these tabs are too flexible they may not hold up under high winds, i.e. may lead to the door becoming disengaged, even in a substantially closed position, from wind or air pressure. Conversely, if the tabs are too rigid, the bottom bar, side columns, or door panel could be damaged if the bottom bar or door panel is impacted by an object, inasmuch as the tabs may fail to release from the side columns upon impact. This inverse relationship can make door design difficult, especially in high wind or high pressure/impact areas—particularly where substantial traffic frequently passes through the opening blocked and unblocked by the door panel.
Regardless of whether the tabs are made to be highly flexible or extremely rigid, objects imparting a great force on the door panel or bottom bar may break the tabs completely away from bottom bar, requiring replacement of the tabs or possibly even the entire bottom bar in order to fully realize the guidance and wind load resistance capabilities of the bottom bar and door panel. In doors where engagement between the tabs and side columns is relied on to provide much of the wind load resistance, the breaking away of the tabs may lead to the door having unsatisfactory wind load resistance capabilities and creating unwanted blow out resulting from normal or even light wind loads.
In some door designs, in addition or instead of tabs, the bottom bar may include a structural steel angle or pivot to increase the flexibility of the bottom bar and/or further facilitate the dislodgment of the bottom bar and door panel should the bottom bar or door panel be impacted by an object. The angle may include, for example, a notch in the middle, and utilize a piece of flat bar and two sheer pins to provide rigidity and resistance to wind and maintain the shape of the bottom bar as the door panel opens and closes. If impacted, however, the sheer pins may break, allowing the bottom bar to bend at the notch and succumb to external forces, for example wind, even when in the substantially closed position. In order to prevent dislodgement of the door panel and/or bottom bar from a wind force once the sheer pins are broke, the bottom bar must be bent back into place and the sheer pins must be replaced.
Therefore, it would be advantageous to provide a device and method capable of providing an overhead roll-up door with satisfactory wind load resistance, particularly when the door panel is substantially or fully closed when the wind load is highest, while providing maximum breakaway-ability of the door panel if any of the door components are impacted.
It would be further advantageous if the device and method contained minimal parts which may otherwise need replacement or repair resulting from breakage because of impact by objects striking the door.
The present invention is directed to solving these and other problems.